Synthesis of methylene butyrolactone polymers from itaconic acid

Herein, we report the transformation of β‐monomethyl itaconate, an inexpensive and biorenewable alternative to petroleum feedstocks, to the high‐value monomer α‐methylene‐γ,γ‐dimethyl‐γ‐butyrolactone (Me₂MBL) through a selective addition strategy. This strategy is also applied to the synthesis of α‐methylene‐γ‐butyrolactone (MBL, tulipalin A), a monomer that can be polymerized to give materials with desirable properties (high decomposition temperature, glass transition temperature, and refractive index). Subsequent polymerization of both Me₂MBL and MBL through reversible addition‐fragmentation chain‐transfer polymerization generates well‐defined poly(Me₂MBL) and poly(MBL) (PMBL). Physical characterization of poly(Me₂MBL) shows good physical properties comparable with known PMBL materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2730–2737     

Merging metathesis and photochemical Csp3-H activation: Access to masked β-formyl hexanolides and their rearrangement to furofuranones

β-Masked formyl hexanolides were prepared by a three-step sequence including esterification of homoallylic alcohols, ring-closing metathesis and the photochemically induced addition of dioxanyl radical. When treated under oxidative conditions, the adducts underwent cleavage of the ketal group leading after rearrangement to parent furofuranones, structures found in some biological active compounds.     

One Amine–3 Tasks: Reductive Coupling of Imines with Olefins in Batch and Flow

Owing to their wide range of biological properties, γ-aminobutyric acid derivatives (GABA) have been extensively studied and found noteworthy industrial applications. However, atom-economical and efficient processes for their production are scarce and would greatly benefit from further investigations. Herein, we demonstrate that an iridium-based photocatalyst promotes the direct reductive cross-coupling of imines with olefins upon irradiation with visible light to give GABA derivatives in good yields and selectivities. We also stress the enabling triple role of tributylamine additive in this process, discuss the advantages of strategies based on proton-coupled electron transfer (PCET) and demonstrate the scale-up of this reaction in continuous flow.     

Chiral Supramolecular Nanotubes of Single-Chain Magnets

We report a single-chain magnet (SCM) made of a terbium(III) building block and a nitronyl-nitroxide radical (NIT) functionalized with an aliphatic chain. This substitution is targeted to induce a long-range distortion of the polymeric chain and accordingly it gives rise to chains that are curled with almost 20 nm helical pitch. They self-organize as a chiral tubular superstructure made of 11 chains wound around each other. The supramolecular tubes have a 4.5 nm internal diameter. Overall, this forms a porous chiral network with almost 44 % porosity. Ab initio calculations highlight that each Tb^III ion possesses high magnetic anisotropy. Indeed, notwithstanding the supramolecular arrangement each chain behaves as a SCM. Magnetic relaxation with both finite and infinite-size regimes is observed and confirms the validity of the Ising approximation. This is associated with quite strong coercive field and magnetic remanence (H_c=2400 Oe M_R=2.09 μ_B at 0.5 K) for this class of compounds.     

All-cis poly(p-phenylene vinylene)s with high molar masses and fast photoisomerization rates obtained through stereoretentive ring-opening metathesis polymerization of [2,2]paracyclophane dienes with various aryl substituents

Poly(p-phenylene vinylene)s (PPVs) are some of the most widely studied conjugated polymers in academia and industry, but most production methods lack precise control over molar masses and alkene stereochemistry. These critical parameters have a large influence on processability, polymer morphology, and optical properties. Herein, we report the stereoretentive ring-opening metathesis polymerization (ROMP) of [2.2]paracyclophane dienes bearing either a linear alkyl substituent or a branched alkoxy substituent to form all-cis PPVs with great solubility in organic solvents. The introduction of 2-ethylhexyloxy side-chains permits the preparation of PPV with uncharacteristically high molar masses (up to 108.8 kg/mol) for a polymerization with living characteristics. Exposure to UV light (365 nm) rapidly induces isomerization of all-cis alkenes leading to the formation of all-trans PPV. This study proposes an attractive strategy to synthesize soluble all-cis and all-trans PPVs with tunable, high molar masses through careful design of the ROMP monomer.     

An Orthogonal Dynamic Covalent Chemistry Tool for Ring-Opening Polymerization of Cyclic Oligochalcogenides on Detachable Helical Peptide Templates

A model system is introduced as a general tool to elaborate on orthogonal templation of dynamic covalent ring-opening polymerization (ODC-TROP). The tool consists of 3₁₀ helical peptides as unprecedented templates and semicarbazones as orthogonal dynamic covalent linkers. With difficult-to-control 1,2-dithiolanes, ODC-TROP on the level of short model oligomers occurs with high templation efficiency, increasing and diminishing upon helix stabilization and denaturation, respectively. Further, an anti-templated conjugate with mispositioned monomers gave reduced templation upon helix twisting. Even with the “unpolymerizable” 1,2-diselenolanes, initial studies already afford mild templation efficiency. These proof-of-principle results promise that the here introduced tool, recyclable and enabling late-stage side chain modification, will be useful to realize ODC-TROP of intractable or unknown cyclic dynamic covalent monomers for dynamer materials as well as cellular uptake and signaling applications.     

Recent advances in integrating platinum group metal-free catalysts in proton exchange membrane fuel cells

Platinum group metal (PGM)-free catalysts are promising low-cost materials for the oxygen reduction reaction in proton exchange membrane fuel cells (PEMFCs). A variety of chemical precursors and synthesis methods have been proposed to increase their catalytic activity. In comparison, significantly less attention has been dedicated to the integration of these PGM-free catalysts into operating electrodes by investigating the role of the membrane electrode assembly (MEA) fabrication on the PEMFC performance. We discuss here some remarkable performance improvements recently achieved by tuning catalyst loading, ionomer content, and ink solvent composition, and call for further explorations of the ink processing and MEA fabrication to improve performance.     

Left-handed properties of erbium-doped crystals

We show that lanthanide-doped crystals can be made left handed for a finite spectral range. The electronic transitions in the dopant ions are both dipolar electric and dipolar magnetic allowed. This enables tuning the permittivity and the permeability at the same frequency. The analysis focuses on erbium-doped crystals where left-handed properties are predicted inside an experimentally reachable domain of parameters.